1. Field of Invention
The present invention relates generally to abdominal wall reinforcement devices, and in particular devices used for the treatment of inguinal hernias by either an anterior or laparoscopic route.
2. Description of the Related Art
Providing a permanent mechanical support for the repair of abdominal wall hernias is well known in the art. Various implants and surgical techniques have been developed to assist surgeons during reconstructive procedures to improve the outcome of such procedures, both in terms of its effectiveness and tolerance by the patient. It is known, for example, that reinforcement of the operative area by a mechanical implant is improved when the implant quickly integrates in the tissue. As disclosed in U.S. Pat. No. 6,596,002 (assigned to Sofradim), to achieve intimate and early integration of the implant without formation of a peripheral fibrous shell, the macroporosities of the implant must be as widely open as possible to the outside and the elasticity of the reinforcement must allow it to follow the physiological deformations of the wall onto which the device is placed. The suitability of such a device is related to the mechanical resistance of the textile material used to form the implant. It is reported that such resistance must be greater than 10 decanewtons using the standardized ISO5081 test. Such devices should prevent hernia recurrence through the pores of the tissue, which must be a maximum of 7 to 10 millimeters in diameter.
The invention disclosed in U.S. Pat. No. 6,596,002, involves a knitted mesh useful for the treatment of inguinal hernias by the anterior access route, which is placed in a premuscular location. The knitted mesh is characterized as affording the practitioner with an implant device that is easy to use, quickly securable in place, and that effectively repairs abdominal wall deficiencies. The knitted mesh includes a reinforcement piece and a flap piece connected to the reinforcement piece. The reinforcement piece is cut from an open-worked prosthetic knit web. The web is made of multifilament yarns. The reinforcement piece includes a radial slit and annular cut-out region approximately in the center of the reinforcement piece that allows the surgeon to place the piece around the spermatic cord. According to the patent, the reinforcement piece has the general shape of an ellipse, and it satisfies the requirements mentioned above. In particular, the shape allows the surgeon to cover all the potential parietal weakness. The device is described as being easy to put into place.
The aforementioned flap piece is made such that it may be folded over the slit on the reinforcement piece to close it. The flap is described as having a “gripping means” integral with the flap itself, or attached to it, for fastening or joining the flap piece to the knitted structure of the reinforcement piece. In one embodiment, the flap is described as having spike naps projecting from its face. The spiked naps are formed by a monofilament yarn and have a length allowing them to penetrate into and attach themselves to the knitted structure of the reinforcement piece without protruding from the latter. That is, on one end, the spiked naps are embedded into the knit web to secure them, and on the other end project above the surface of the flap piece, generally extending above the plane of the flap piece in a perpendicular direction. Depending on the particular applications for the device, the spike naps are made of a biocompatible polymer or of bioabsorbable material, such as polylactic acid (PLA). In use, the flap is folded over the reinforcement piece such that the spiked naps engage in and between the multifilament yarns of the knit of the reinforcement piece, similar to a hook and loop fastener. This ensures that the flap piece is locked in position, securely closing the slit and holding the spermatic cord in position. The spiked naps are not permanent, however. The flap piece may be unfastened and repositioned, if necessary.
The density of the spiked naps is reportedly determined as a function of the prosthetic knit being used, but is reportedly best in the range of between 50 and 90 naps per cm2. The length of the naps, measured from the base projecting from the attachment sheet to the top of the spike, will depend on the thickness of the prosthetic knit forming the reinforcement piece, but is reportedly best in the range between 1 and 2 millimeters.
In the aforementioned patent, the reinforcement piece is described as having a grip or gripping means, which is integral with the knit or attached to it, and is used for fastening or joining. The same spiked naps described above may be used on one face of the reinforcement piece, just as they are used on the flap piece. The grip/gripping means devices project from one and/or the other of the faces of the knit, and are used to fasten or join the reinforcement piece to the tissues the device is place in contact with. The knit from which the reinforcement piece is made is described as a “flat knit” type or one having two porous layers connected by connecting yarns. The weave of the knit forms run-proof transverse channels opening out from the two porous layers.
A commercial embodiment of the knitted mesh device called ProGrip™ is available from Covidien (Massachusetts). Its use is described in Philippe Chastan, M.D., “Tension-Free Open Inguinal Hernia Repair Using an Innovative Self Gripping Semi-Resorbable Mesh,” published in the Journal of Minimal Access Surgery, 2006 (see pp 139-43 describing results based on a published study of the Parietene™ (polypropylene) version of the ProGrip™). In its literature, Covidien states that the biocompatible monofilament knit making up the knitted mesh is made from non-resorbable polyethylene terephthalate (PET), and the spike naps are made from a resorbable poly lactic acid (PLA). The monofilament knit is hydrophilic, so it works with the body's natural systems to improve tissue integration while reducing foreign material response. The entire mesh with the spike naps reportedly provides “immediate fixation” to the underlying tissue. The knit material is substantially stronger than using fibrin glue, and is equivalent to incorporation by hernia stapler fixation at five days after placement. Compared to suture fixation, the device is 100% stronger at four weeks. The literature also notes that the device can be positioned and placed in less than 60 seconds, and unlike standard open repair of parietal deficiencies, the device does not require additional fixation methods. The device has a reported density of 73.0 g/m2 before resorption of the spiked naps, and a reported density of 38.0 g/m2 after resorption (a change of 53 g/m2 or 48-percent).
Despite the features and advantages of the invention described above, experience has shown that the spike naps may adhere too quickly for some applications, i.e., “immediate fixation” or adherence in less than 60 seconds. Removing the device (so it can be repositioned) is difficult after attachment, and it can be traumatic to the underlying tissue. Often, repositioning cannot be done, so a new device is requires, at relatively substantial expense to the patient or practitioner. Also, the device is expected to attach quickly to intra-abdominal tissues (e.g., smooth tissues such as bowel), and so the device is not useful for intra-abdominal implantation using, for example, laparoscopy instruments to place the device interiorly of, for example, an abdominal wall hernia. Accordingly, there exists a need for such a device.
It is well known in the medical arts to apply a measured amount of a spreadable “gel” to form a temporary layer, which may then provide the benefit of protecting, at least temporarily, another layer, material, or object, or to reduce the friction between two surfaces separated by the gel layer. Such a gel, if applied to the spiked naps of the aforementioned product, would reduce the gripping ability of the spiked naps and allow the practitioner to place and then replace the knitted mesh device before the spiked naps begin to adhere to the parietal tissues. However, if the gel has a high viscosity, the ability of the spiked naps to be reabsorbed by the underlying tissue may be greatly reduced, causing the knitted mesh to be too loose and require additional sutures. Also, low viscous gels are unsuitable from a manufacturing perspective, because they are difficult to apply to a mesh, and would require special or different packaging materials compared to a knitted mesh without a gel layer. Further, many gels may be easily disturbed by the practitioner's fingers and/or instruments used by the practitioner, thereby reducing or eliminating their effectiveness.
It is also well known in the medical arts to use adhesives to attached a device to a patient or substrate. An adhesive layer applies to the knitted mesh and/or spiked naps of the aforementioned device would immediately cause fixation, making it more difficult to remove or reposition. Also, unlike the spiked naps of the aforementioned knitted mesh device, an adhesive is generally not reabsorbed (at least not immediately), and so it can form (at least temporarily) a generally impenetrable layer between the device and the underlying tissue, which may not be desirable in certain applications.
It is also known in the medical arts to use a removable, protective film or layer over another layer. Thus, a film could be used over an adhesive layer on a device that prevents the adhesive from sticking until the device is used. Such protective films are relatively inexpensive to make from various inert, compatible, and stable polymeric materials. In use, the practitioner simply removes and discards the film, then positions the device and permanently places it using the underlying adhesive to hold the device in place. Adding a film to an adhesive layer may be feasible, but it may not be suitable for adding directly to the knitted mesh device described above without at least some adhesive between the file and underlying PET knit and PLA spiked naps extending from the knit. If the film attaches to the spiked naps, it may not be cleanly removable without destroying some of the spiked naps, thereby reducing the effectiveness of those devices for their intended purpose. Also, removing the film intra-abdominally presents all sorts of challenges to the practitioner and is, practically speaking, not feasible (i.e., the film would have to be removed exteriorly of the patient).
Accordingly, there exists a need for a material that reduces the time before the spiked naps of the aforementioned invention begins to adhere and reabsorb in the tissue so that it can be removed and repositioned quickly, is suitable for manual placement by a practitioner's fingers or using a laparoscopy instrument, and is relatively inexpensive to manufacture.